Recently, a head-mounted display capable of presenting stereoscopic videos of depth has been popularized on the basis of the development of technologies for presenting stereoscopic videos. The head-mounted displays are capable of presenting videos of depth to users and used as three-dimensional (3D) content presentation devices, such as 3D movies and 3D games, for example.
A head-mounted display is worn on a user who is a watcher such that both eyes of the user are covered. Some head-mounted displays are of shielding type that videos are presented by shielding the outside world from the field of view of the user upon wearing on the user. In a situation with a head-mounted display of such shielding type worn, it is often difficult for the user to look at a real video in the outside world. Therefore, some of the head-mounted displays of shielding type each have a camera for taking an image of the outside world.